An immersion freezer

Abstract: A substantially 'U' shaped immersion freezer (10) is provided with an inlet (14) and an outlet (16) at either end thereof and a freezing zone (20) filled with liquid nitrogen at the bottom thereof. food product to be frozen is dropped into the freezer and raised to the outlet by paddle member (24). The frozen food product and some liquid nitrogen (22) is then passed to a conveyor (34) having holes provided therein which allow the liquid nitrogen to be drained from the food product for recycling back to the inlet side of the freezer (10).

Description: The present invention relates to immersion freezers and relates particularly, but not exclusively, to immersion freezers suitable for freezing food product. Presently known immersion freezers comprise a perforated conveyor which is, along at least part of its length, dipped into a bath of liquid refrigerant, such as liquid nitrogen. The liquid nitrogen acts to freeze the product before it is removed from the bath. In order to enable the conveyor to be snaked into and out of the liquid nitrogen and to ensure that the residence time of the product under the surface of the liquid nitrogen is sufficient to avoid under chilling, the bath must be somewhat larger than desired. It will be appreciated that the larger the bath the greater the volume of liquid nitrogen and hence the greater the waste thereof. Additionally, handling large quantities of liquid nitrogen safely can be a problem. Further to this, the conveyor can become blocked with ice and/or small particles of food product and must be removed from the liquid nitrogen for cleaning. Clearly, it will be impossible to continue operating the machine during cleaning. An alternative immersion freezer is provided with a continuous belt which in one direction is passed through a bath of liquid nitrogen and in the other direction is passed underneath the bath itself, thereby avoiding further immersion in the liquid nitrogen. In this arrangement, it is also known to shape the bath such that the belt drops vertically into the front of the bath and is raised gradually from the rear thereof. Such an arrangement reduces the overall bath volume and hence reduces slightly the problems of liquid waste and safe handling. However, it is obviously impossible to lift the belt out of the liquid nitrogen for cleaning. An additional problem associated with the above mentioned arrangements resides in the fact that undesirable liquid 'boil off occurs due to the cyclic cooling and heating of the conveyor as it passes into and out of the liquid nitrogen. US-A-2552029, which is considered to be the closest prior art, discloses a cold treating machine in which objects to be cooled are pushed against each other along and round a U-shaped guide-way extending into a bath of liquid refrigerant. WO-A-8910522 discloses a device for producing and projecting balls of ice for surface treatment purposes, the balls being extracted by a screw from a bath of liuqid refrigerant in which they are formed. EP-A-0611928 relates to the coolng of lumpy or granular material by passing the material through a U-shaped pipe immersed in liquefied gas, the lumps being pressed together and along the pipe by a ram device. It is an object of the present invention to reduce and possibly eliminate the problems associated with the prior art arrangements. Accordingly, the present invention provides an immersion freezer comprising an inlet for receiving product to be frozen, an immersion zone, for containing a liquid refrigerant and through which product is passed for freezing thereby, and an outlet, through which frozen product is extracted from the freezer, in which the freezer comprises a generally U-shaped tube the ends of which act to define the inlet and outlet respectively and the lower portion of which acts to define the immersion zone, said tube being adapted for receiving product in a manner which allows product to fall to the bottom of the tube and provided with transportation means for transporting product from said bottom to the outlet, characterised in that the transportation means comprises one or more paddle members for causing an upward flow of liquid refrigerant between the bottom and the outlet of the tube thereby to at least assist in the extraction of product from the tube, and to raise the level of liquid refrigerant on the outlet side higher than that on the inlet side. It will be appreciated that by making use of a 'U' shaped tube rather than a large bath, it will be possible to reduce significantly the quantity of liquid nitrogen being used. Additionally it is not necessary to provide a conveyor passing into and out of a bulk of liquid nitrogen, thereby avoiding the problems associated therewith. Preferably, the inlet is provided in the upper surface of the U-shaped tube which is thereby adapted for allowing product to fall directly to bottom of the tube. Preferably, the transportation means comprises a plurality of paddles circumferentially and/or axially spaced along a shaft extending into the U-shaped tube at the outlet end thereof, said shaft being rotatable to cause movement of the paddles and hence movement of the liquid refrigerant. Alternatively, the transportation means comprises a spiral paddle member. Preferably, the freezer further including extraction means for extracting product from the outlet end of the tube and directing it to a conveyor for conveying product away from the freezer Advantageously, the extraction means comprises a scoop for scooping product off the surface of the liquid refrigerant at the outlet end of the tube and for directing said product towards the conveyor. Preferably, the freezer further includes a conveyor for conveying product away from the freezer. Advantageously, the freezer further includes recycling means for recycling liquid refrigerant extracted with the product back to the inlet side of said tube. In a particularly advantageous arrangement the recycling means comprises the conveyor and a liquid return chute, said conveyor being provided with a plurality of holes therein for the passage of liquid refrigerant therethrough and said return chute being positioned for receiving liquid refrigerant drained from product being frozen. Conveniently, the conveyor passes between the inlet and the outlet of the U shape tube and the liquid return chute is positioned beneath said conveyor. The present invention will now be more particularly described by way of example only with reference to the accompanying drawings in which: Figure 1 is a cross-sectional view of an immersion freezer according to the present invention; and Figure 2 is an isometric projection of the freezer shown in cross-section in Figure 1. Referring now to the drawings in general, but particularly to Figure 1, an immersion freezer 10 comprises a generally 'U' shaped tube 12 having an inlet 14 at a first end and an outlet 16 at a second end. The lower portion 18 of the tube 12 acts to define an immersion zone 20 filled with liquid nitrogen 22. The inlet 14 and outlet 16 are shown at the end of the U, however, it will be appreciated that one or other of them could be positioned at the side thereof. A transportation means 24 in the form of, for example, a spiral paddle member 26 or a plurality of individual paddles circumferentially and axially spaced from each other (not shown) is provided in the outlet side of the tube 12. The paddle member is mounted on a rotatable shaft 28 and driven by motor 30. An extraction means in the form of chute 32 is provided adjacent to the outlet for directing frozen product towards a conveyor 34, which acts to take the product away from the freezing apparatus. A plurality of holes 36 are provided in the conveyor to allow any liquid nitrogen deposited thereon to pass therethrough and onto a liquid return chute 38 positioned for receiving excess liquid nitrogen from the outlet and returning it to the inlet side of the tube. The chute itself extends between two holes 40 and 42 provided on the outlet and the inlet sides respectively. The operation of paddle member 26 acts to raise the level of nitrogen on the outlet side higher than that on the inlet side and hence the chute 38 can extend generally downwardly between a position just below the surface 39 of liquid nitrogen at the outlet side to a position just above the surface 39 of liquid nitrogen at the inlet side. This arrangement allows the chute to return liquid nitrogen without pump assistance. A level monitor in the form of, for example, a bubbler and back pressure monitor 44, 46 respectively is provided for monitoring the nitrogen level so as to facilitate level maintenance via valve 48 connected to a source of liquid nitrogen (not shown). In operation, food product is dropped into inlet 14 where it sinks to the bottom of the immersion zone 20 partially under gravity and partially due to the action of the transportation means 24 which draw liquid nitrogen and food product from the lower portion of the tube and raise it above the level of liquid nitrogen at the inlet side. Food product, once raised to the surface at the outlet side, is scooped off the surface and directed down chute 32 and onto conveyor 34 which acts to take it away from the freezer. Excess nitrogen is passed through the holes 36 provided in the conveyor and onto chute 38 for recycling. Clearly, as the present arrangement avoids the use of a conveyor passing into and out of a bulk of liquid nitrogen, the problems associated therewith are avoided. Only excess liquid nitrogen is passed through the conveyor 34 and whilst this will cause a certain amount of crust freezing it will not be as severe as in the prior arrangements. It will be appreciated that by separating the conveyor 34 from the bulk of the liquid nitrogen used for chilling purposes it will be possible to clean the belt without having to drain the freezing zone of liquid nitrogen. Additionally, it will be possible to clean the freezing tube 12 without first removing the conveyor 34.

Claims: An immersion freezer (10) comprising an inlet (14) for receiving product to be frozen, an immersion zone (20) for containing a liquid refrigerant (22) and through which product is passed for freezing thereby and an outlet (16) through which frozen product is extracted from the freezer, the freezer (10) comprising a generally U-shaped tube the ends of which act to define the inlet (14) and outlet (16) respectively and the lower portion of which acts to define the immersion zone (20), said tube being adapted for receiving product in a manner which allows product to fall to the bottom of the tube and provided with transportation means (24) for transporting product from said bottom to the outlet (16), characterised in that the transportation means (24) comprises one or more paddle members (26) for causing an upward flow of liquid refrigerant between the bottom and the outlet (16) of the tube thereby to at least assist in the extraction of product from the tube, and to raise the level of liquid refrigerant on the outlet side (16) higher than that on the inlet side (14). An immersion freezer as claimed in Claim 1 characterised in that the inlet (14) is provided in the upper surface of the U-shaped tube which is thereby adapted for allowing product to fall directly into the bottom of the tube. An immersion freezer as claimed in Claim 1 or Claim 2 characterised in that the transportation means (24) comprises a plurality of paddles (26) circumferentially and/or axially spaced along a shaft extending into the U-shaped tube at the outlet (16) end thereof, said shaft being rotatable to cause movement of the paddles (26) and hence movement of the liquid refrigerant. An immersion freezer as claimed in Claim 1, Claim 2 or Claim 3 characterised in that the transportation means comprises a spiral paddle member (26). An immersion freezer as claimed in any preceding Claim characterised by extraction means (32) for extracting product from the outlet (16) end of the tube and directing it to a conveyor (34) for conveying product away from the freezer (10). An immersion freezer as claimed in Claim 5 characterised in that the extraction means comprises a scoop (32) for scooping product off the surface (39) of the liquid refrigerant at the outlet end of the tube and for directing said product towards the conveyor (34). An immersion freezer as claimed in Claim 5 or Claim 6 characterised by a conveyor (34) for conveying product away from said freezer. An immersion freezer as claimed in any preceding Claim characterised by recycling means (38) for recycling liquid refrigerant extracted with the product back to the inlet side of said tube. An immersion freezer as claimed in Claim 8 characterised in that the recycling means comprises the conveyor (34) and a liquid return chute (38), said conveyor (34) being provided with a plurality of holes (36) therein for the passage of liquid refrigerant therethrough and said return chute (38) being positioned for receiving liquid refrigerant drained from product being frozen. An immersion freezer as claimed in Claim 9 characterised in that the conveyor (34) passes between the inlet (14) and the outlet (16) of the U-shape tube and the liquid return chute (38) is positioned beneath said conveyor (34).

Inventors: WARDLE DAVID GRANT, WARDLE, DAVID GRANT
Applicants: BOC GROUP PLC, THE BOC GROUP PLC
Application year: 1994
Main classification: F25D3
IPC codes: A23L3, F25D3, F25C1